Trans RINA, Vol 156, Part C1, Intl J Marine Design, Jan –Dec 2014 the seatbelt, hence the airbag, classified as a
supplementary restraint system, works with the seatbelt to reduce occupant decelerations [17]. In the US, some states still allow occupants to drive without a seatbelt, hence the legal safety test in FMVSS208, which assesses the viability of a vehicle
unbelted 50th percentile driver [18] [19] . Statistics have shown that 41% of occupants in unbelted accidents were killed or seriously [20]. As passengers in the proposed vessel is 40knots (20m/s), which is
airbag at 25mph with an higher than the
FMVSS208 unbelted test speed, it is expected that some serious injuries may be expected.
Figure 24: Occupant position during impact (2.0s)
It has to be noted that the crash test dummies do not have bio-fidelic joints, neck and spine representations as such the distances computed may vary for a human being. This model has however the benefits to have an estimate based on a dummy based on comparable body masses.
7 DISCUSSION The study
discussed in this paper researched the
crashworthiness mechanisms of a 130.0m trimaran against a rigid wall, based on computer simulations.
The complexity of the FEA model proved challenging and focused on a fixed structure, being the worst case scenario with the vessel structure having to absorb all of the kinetic energy [16]. Due to the size of the vessel in terms of displacement the crash event duration,
which is significantly
had a 1.0s longer than an
automotive crash event which contains considerably less structure and kinetic energy to dissipate. This resulted in significant analysis processing time. The complexity of the pre-process meshing due to the size of the CAD model requiring a large number of elements required a macro to be developed in HyperMesh to resolve meshing issues identified through lack of initial model convergence during initial analysis.
The structural collapse deformed the bow 14.0m within the crash bulkhead, containment of deformation and rupture within this area ensured the hydrostatic integrity of the vessel for post crash evacuation of passengers. This localisation effect of deformation may enable a simplified lump parameter model to be used to expedite the analysis process. Reducing the model to a single mass attached to the crash bulk head area would significantly reduce structural modelling allowing design variations on the crash bulk head section to be evaluated. This modelling simplification would ignore the structurally induced characteristics of longitudinal stress waves, and would therefore have to be validated against a full FEA model in given load conditions.
Vehicle safety is looking into vehicle intrusions and the reduction of forces sustained by the occupant. The former being key, as excessive intrusions will lead to severe injuries. In the European market, it is law to wear
OEM use computer models to assess vehicle structures, in order to tune the vehicle architecture and the restraint system for crash test dummies. These tests follow the legislative requirements, as well as other consumer tests, like EuroNCAP which set a standard protocol to meet. The real challenge is that these crash test dummies, although very useful reference engineering tools, do not represent the real trauma people are experiencing, which are gender, age and pre-medical condition specific. In the near future, human computer models will push further the boundaries of safety. The initial occupant crash simulation requires further validation as the thrown away distance is very large compared to a simple unbelted car driver [21] [22]. The thrown distance of up to 50.0m could lead to occupants impacting each other, as they are not restrained to the vessel, which could cause severe trauma
and would be potentially worse for seated
occupants or occupants standing in restricted spaces where they would strike surfaces or other passengers [23]. These values suggest a very severe impact, however it has to be noted that the computer model used only contained thick aluminium sheet metal and no upholstery, hence the real values are likely to be less. Nevertheless this type of impact configuration looks
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©2014: The Royal Institution of Naval Architects
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